Microfluidic needle devices generally comprise a microfluidic channel manufactured to silicon or polymer substrate. Conventional microneedles contain one single hole in one needle. To increase the throughput of fluid through the device or to provide parallel injection of several substances, there may be provided an array of microneedles. Microneedle arrays are known, for example, from US 2007/0233016, disclosing a device with a supporting pad and a plurality of microneedles having slant or concave tips. Also EP 1183064 discloses a microneedle array.
Microneedle arrays have the disadvantage that they take relatively much space on the substrate in relation to the throughput achieved. In addition, very local simultaneous injection and sampling of fluid is not possible.
WO 00/16833 discloses a surface-machined microneedles fabricated “horizontally” on a substrate and a multilumen microneedle having a plurality of microchannels. Such design is difficult to implement such that the microchannels would be ordered in two dimensional configuration.
KR 20020081743 discloses a single-crystal silicon microneedle which may have a plurality of individual microchannels, i.e., a so-called multiport microneedle. The microchannels are located parallel to each other and have their exits on a slanted tip of the needle.
EP 1967581 discloses CMOS-compatible microneedle structures. There is disclosed a microneedle structure wherein a microfluidic channel and filled conductor channel acting as a sensing or actuating electrode are integrated into a single needle.
US 2009/0093776 discloses microneedle structures in which the microchannel exits are located at least partly on a slanted surface of the needle, relatively wide and therefore accessible directly from the top of the needle. Such structure is prone to clogging and does not allow transport of fluids to/from to the vicinity of the tip of the needle.
EP 1652551 discloses completely different microneedle type, in which there are no inner microchannels at all, but the channels are formed as slanted groove open to the sides of the microneedle along the whole length of the needle. Also such structure is prone to clogging.
One-channel needles are disclosed in EP 1669100, WO 2003/015860 and WO 2008/027011.
The approaches referred to above have disadvantages, one of which is the clogging of the needles. As the size of the microfluidic channels is reduced, as is necessary in the case of multichannel needles, even smaller particles will stick to the channels and prevent fluid flow fully or partially. In addition, as the exits of the needle are located very close to each other, simultaneous injection and sampling are directed to a very local area, whereby sampling may not give reliable results in certain applications.